This invention relates to improvements in mobile material distribution apparatus such as those used in the spraying of fertilizers, weed killers, insecticides, or the like. While the invention may be useful in a wide variety of applications, the ensuing description will be facilitated by specific reference to hand-pushed mobile spray apparatus, and the problem of maintaining a uniform and selectable distribution rate of liquid in spray form over an area to be treated.
Many areas of agriculture apply materials such as fertilizers, weed killers and insecticides in a liquid form and distribute this liquid by spraying it over an area to be so treated using what is commonly known as a "sprayer". Typically, the liquid is pumped through hoses to multiple spray nozzles which are attached to an elongated bar or "boom". The boom permits the implementation of multiple nozzles to spray at higher rates over a larger area as the device is propelled along a given path of travel, thereby reducing the time required to spray a given total field area, making the operation more efficient. Large booms are often towed behind a tractor or similar vehicle, while smaller versions are hand-pushed by an operator.
Some of the hand operated sprayer applications include: spraying steep areas where a tractor is unable to operate safely; spraying delicate areas such as golf greens or newly planted areas where a tow vehicle could cause damage to the surface being sprayed; spraying areas which are inaccessible to a towing vehicle but which are for some reason large enough to require a boom sprayer to efficiently complete the spraying job, such as areas which are accessible only by narrow roads or trails; and/or areas which require tighter maneuvering than is possible with a tow vehicle. In the above situations the material to be sprayed is fed to the sprayer through a hose from a reservoir such as a towed tank trailer or the like.
Controlling distribution rates and spray patterns of these liquids is important. Controlling distribution rates and spray patterns improves the cost efficiency of the operation by avoiding spraying more or less liquid than is needed on a given area. For example, in spraying fertilizer on a grassy area such as a lawn or golf course, controlling the rate of distribution and spray pattern prevents killing the grass by spraying too much fertilizer and also prevents aesthetically offensive striping caused by fertilizer overlap.
In all the above-mentioned sorts of spraying operations, the nozzle spray pattern and position of the nozzle relative to the spray surface are important factors in applying the spray in a well-controlled manner. The nozzle spray pattern is normally controlled by selection of the type of nozzle to be used. However, control of the spray pattern also requires control of the position of the nozzle relative to the surface being sprayed, and this has caused many problems for prior art spraying systems.
A problem with many prior art spray systems is that they travel across the spray surface on two wheels mounted on a single axle. Two-wheeled apparatus tend to tip forward and backward about the axis of the axle, raising and lowering the spray nozzle throughout the spraying operation thus changing the spray pattern by changing the angle and height of the spray nozzles.
One prior art device recognized the problems caused by variations in spray boom height and the need to fixably raise or lower the spray boom. The prior art apparatus, the Walking Boom manufactured by FMC Agricultural Machinery Division, Jonesboro, Arkansas, provides a boom perpendicularly mounted to a tube structure which fits over a smaller diameter tube mounted to the axle of the apparatus. The larger tube is fitted with spring pins which lock into holes in the smaller diameter inner tube. While the structure of the apparatus provides adjustability of boom height, it is subject to the forward and backward tipping problem inherent in two-wheeled sprayers. Therefore, because of the tipping problem of the two-wheeled design, the adjustment feature does not solve the problem of maintaining a constant spray boom height above the spray surface. Another problem with such two-wheeled sprayers is that they do not easily track a consistent path. The two-wheel apparatus tends to "waddle" while being manually pushed, causing a wavy spray-distribution path. Waddling occurs when slightly greater force is applied to one side of the handle than the other, causing a faster rotation about one wheel than the other. When the rotation has progressed to a noticeable point, the operator usually compensates and turns the apparatus back on the desired path. Compensation usually results in over-compensation and waddling results. Waddling causes a wavy application of material and fatigues the operator more quickly than if he could maintain a more consistent spray path.
Yet another problem with the prior art apparatus is that the two-wheeled design is difficult to leave unattended or "parked". To park the two-wheeled apparatus the user has three choices: (1) rest the spray apparatus on the nozzles; (2) rest the spray apparatus on its handle; or (3) rest the spray apparatus against another fixed surface. Resting the spray apparatus on its nozzles or handle could easily result in damage to the apparatus and resting the sprayer on another surface is usually inconvenient, e.g. suitable surfaces are not always available.
Further, the inability of the prior art sprayer to stand unattended makes the sprayer difficult to erect after being stored. That is, many of the prior art units provide for foldable booms to make the units easier to store. However, the user must lean the apparatus against a fixed surface to unfold the booms and erect the apparatus. Since the two-wheeled unit is unstable, it could slip off the surface it is leaning against potentially resulting in damage to the unit.